[gcc r15-9532] c++: format attribute redeclaration [PR116954]

[Jason Merrill via Gcc-cvs]

https://gcc.gnu.org/g:b0d7d644f3c25af9bf60c948ab26aa7b09a68787

commit r15-9532-gb0d7d644f3c25af9bf60c948ab26aa7b09a68787
Author: Jason Merrill <ja...@redhat.com>
Date:   Wed Apr 16 11:15:14 2025 -0400

    c++: format attribute redeclaration [PR116954]
    
    Here when merging the two decls, remove_contract_attributes loses
    ATTR_IS_DEPENDENT on the format attribute, so apply_late_template_attributes
    just returns, so the attribute doesn't get propagated to the type where the
    warning looks for it.
    
    Fixed by using copy_node instead of tree_cons to preserve flags.
    
            PR c++/116954
    
    gcc/cp/ChangeLog:
    
            * contracts.cc (remove_contract_attributes): Preserve flags
            on the attribute list.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/Wformat-3.C: New test.

Diff:
---
 gcc/cp/contracts.cc                   |  6 +++++-
 gcc/testsuite/g++.dg/warn/Wformat-3.C | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/contracts.cc b/gcc/cp/contracts.cc
index f2b126c8d6be..3ca2102e8663 100644
--- a/gcc/cp/contracts.cc
+++ b/gcc/cp/contracts.cc
@@ -863,7 +863,11 @@ remove_contract_attributes (tree fndecl)
   tree list = NULL_TREE;
   for (tree p = DECL_ATTRIBUTES (fndecl); p; p = TREE_CHAIN (p))
     if (!cxx_contract_attribute_p (p))
-      list = tree_cons (TREE_PURPOSE (p), TREE_VALUE (p), list);
+      {
+       tree nl = copy_node (p);
+       TREE_CHAIN (nl) = list;
+       list = nl;
+      }
   DECL_ATTRIBUTES (fndecl) = nreverse (list);
 }
 
diff --git a/gcc/testsuite/g++.dg/warn/Wformat-3.C 
b/gcc/testsuite/g++.dg/warn/Wformat-3.C
new file mode 100644
index 000000000000..e308530761c9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wformat-3.C
@@ -0,0 +1,19 @@
+// PR c++/116954
+// { dg-additional-options -Wformat }
+
+#ifndef WORKS
+template<int N>
+int fn(char (&buf)[N], const char fmt[], ...)
+  __attribute__ ((__format__ (__printf__, 2, 3)));
+#endif
+
+template<int  N>
+__attribute__ ((__format__ (__printf__, 2, 3)))
+int fn(char (&)[N], const char [], ...)
+{ return 0; }
+
+int main()
+{
+  char buf[20];
+  return fn(buf, "%s", 42); /* { dg-warning "Wformat" } */
+}